The primary objective of the proposed research is the construction of a typing system with adequate resolution for the identification of individual strains of S. sanguis. The system will be based upon the ability of individual strains to inhibit the growth of a unique group of sensitive indicator bacteria and upon the sensitivity of individual strains to particular combinations of inhibiting bacteria. The typing procedure is designed for the qualitative identification of strains and not for enumerating them in situ. The methodology is based on bacteriocin inhibition. 0.1 ml of a log culture of S. mutans in 2.5 ml of melted brain heart infusion-yeast extract agar is flooded onto a plate of BHIYE agar. After drying a six hour culture of bacteriocin producer is stabbed through the lawn into the plate. After overnight incubation at 37 degrees Centigrade, inhibition of Lawn growth is seen as a clear zone. Goals for the current year include: 1. Selection of bacteriocin-producers for inclusion in strain typing sets. 2. To determine which strains of S. sanguis inhibit the growth of a select group of S. mutans. This goal is an extension of the goal listed first, which included an assay of S. sanguis for inhibition S. mutans. 3. Recognition of bacteriocin-producing microorganisms which could be used to strain type S. mutans. This work was not included in the original plan; however, numerous colleagues have requested that I initiate this work. Moreover, this extension fit very nicely into the procedures of the overall project.